FoxA proteins regulate H19 endoderm enhancer E1 and exhibit developmental changes in enhancer binding in vivo

Multiple enhancers govern developmental and tissue-specific expression of the H19-Igf2 locus, but factors that bind these elements have not been identified. Using chromatin immunoprecipitation, we have found two FoxA binding sites in the H19 E1 enhancer. Mutating these sites diminishes E1 activity in hepatoma cells. Additional chromatin immunoprecipitations show that FoxA binds to E1 in fetal liver, where H19 is abundantly expressed, but that binding decreases in adult liver, where H19 is no longer transcribed, even though FoxA proteins are present at both times. FoxA proteins are induced when F9 embryonal carcinoma cells differentiate into visceral endoderm (VE) and parietal endoderm (PE). We show that FoxA binds E1 in VE cells, where H19 is expressed, but not in PE cells, where H19 is silent. This correlation between FoxA binding and H19 expression indicates a role for FoxA in regulating H19, including developmental activation in the yolk sac and liver and postnatal repression in the liver. This is the first demonstration of a tissue-specific factor involved in developmental control of H19 expression. These data also indicate that the presence of FoxA proteins is not sufficient for binding but that additional mechanisms must govern the accessibility of FoxA proteins to their cognate binding sites within the H19 E1 enhancer.     

Nuclear factor EF-1A binds to the adenovirus E1A core enhancer element and to other transcriptional control regions.

We have identified a cellular enhancer-binding protein, present in nuclear extracts prepared from human and rodent cells, that binds to the adenovirus E1A enhancer element I sequence. The factor has been termed EF-1A, for enhancer-binding factor to the E1A core motif. EF-1A was found to bind to two adjacent, related sequence motifs in the E1A enhancer region (termed sites A and B). The binding of EF-1A to these adjacent sites, or to synthetic dimerized sites of either motif, was cooperative. The cooperative binding of EF-1A to these sites was not subject to strict spacing constraints. EF-1A also bound to related sequences upstream of the E1A enhancer region and in the polyomavirus and adenovirus E4 enhancer regions. The EF-1A-binding region in the E1A enhancer stimulated expression of a linked gene in human 293 cells when multimerized. Based on the contact sites for EF-1A binding determined by chemical interference assays, this protein appears to be distinct from any previously characterized nuclear binding protein.